High temperature lubricant comprising fibrous glass



United States Patent 3,113,105 HKGH TEMPERATURE LUBRICANT COMPRISING FlilROUS GLASS Games Slayter, Newark, and Richard F. @hannon, Lancaster, Ohio, assignors to Owens-Corning Fiherglas Corporation, a corporation of Delaware No Drawin Filed June 28, 1961, Ser. 120,202 7 Claims. (Cl. 252-13) This invention relates to a high temperature lubricant, and, more particularly, to a silicone fluid lubricant that is effective at high temperatures because of the dispersion therein of short lengths of small diameter coated glass fibers.

At the present time there exists a substantial need for lubricants which are effective at elevated temperatures. Such lubricants are required for use in conjunction with moving parts which must operate at high temperatures, and sometimes also at high speeds. It has been stated by one authority in the field that a lubricant effective at tempertaures between 600 F. and 700 F. would constitute a major technical advance. One of the serious problems that is encountered in attempting to lubricate moving parts at high temperatures is the extremely low viscosity of available lubricants; which makes containment thereof extremely difiicult, if not impossible. The problem that must be solved is that of increasing the high temperature viscosity of the lubricant without destroying its ability to lubricate, either at high temperatures or at low temperatures.

The present invention is based upon the discovery that short lengths of coated small diameter fibrous glass, when dispersed in a silicone fluid, substantially increase the high temperature viscosity thereof, without appreciably afiecting either the high temperature or the low temperature lubricating characteristics thereof.

It is, therefore, an object of the invention to provide an improved lubricant.

It is a further object of the invention to provide a lubricant effective at high temperatures because of the dispersion therein of short lengths of coated small diameter glass fibers.

Other objects and advantages will be apparent from the description which follows, which is intended only to illustrate and disclose, but in no way to limit the invention.

According to the invention an improved lubricant is provided. Such lubricant comprises short lengths of fibrous glass having diameters not greater than about 5 microns, a higher fatty acid lubricous coating tightly adhered to at least a pant of the surface of each of the lengths of fibrous glass, and a silicone fluid lubricant, the coated lengths of fibrous glass being dispersed in the silicone. Glass beads or spheres having a diameter up to about 7 microns, and having a lubricous coating, can also be dispersed in such lubricant.

It is believed that there is no theoretical lower limit on the diameters of the lengths of fibers dispersed in a lubricant composition in accordance with the invention. It has been found that fiber lengths having a diameter greater than about 5 microns are unsatisfactory because they cause abrasion of a part which it is desired to lubricate. However, at least within the limits of presently available fiber diameters, this Variable seems to be unimportant so long as diameter is less than about 5 microns. Even extremely small diameter fibers which have become available by virtue of recent technological advances in the art of fiber production have been found to be equally as effective as those of relatively larger diameter, up to about the 5 micron limit. As a practical matter, however, there is probably no reason to employ fibers having a diameter smaller than about 0.05 micron.

It has also 'been found that only relatively short lengths of small diameter fibers are effective at producing a lubricant in accordance with the invention. It. is difficult to produce a uniform dispersion of relatively long fibers in a silicone fluid. It is usually preferred that the fiber lengths be from about 0.0003 inch to about 0.25 inch i.e. from about 7.5 microns to about 6000 microns, and most desired that they be from about 0.0003 inch to about 0.001 inch. Fibers of such lengths can be produced conveniently by placing fibers of appropriate diameter and any convenient available length and form in a beater of the type commonly employed in the paper industry to produce uniform dispersions of pulp and water. Appropriately sized fibers are produced in such apparatus after about 10 to 15 minutes of beating, which is usually advantageously carried out in the presence of water. The chopped fibers can then be separated from the water and dried.

It has been found that effective high temperature lubricants can be produced having as little as about /2 percent of coated glass fibers in a silicone fluid lubricant, or as much as about 15 percent thereof, based on the total of fibers and silicone. Optimum high temperature lubricants have been produced from fibers having diameters of about micron where the fiber content was from about 2 percent to about 10 percent.

The terms percent and parts are used herein, and in the appended claims, to refer to percent and parts by weight, unless otherwise indicated.

The term higher fatty acid is used herein and in the appended claims in its usual sense to refer to monohydric acids having from 10 to 20 carbon atoms, including saturated acids which have the generic formula C I-1 0 similar unsaturated acids, alicyclic acids and naphthenic acids which are obtained from petroleum.

Electron microscope photographs of glass fibers, that have been mixed with a suitable lubricating fluid containing a minor amount of a higher fatty acid to produce a lubricant, indicate that a coating forms on the surface of the fibers during high temperature service. Such coating is lubricous, and is not dissolved by solvents for the lubricating medium. It is believed, therefore, that chemical reaction takes place between the higher fatty acid constituent of the lubricating fluid and the glass surfaces to form such lubricous coating, and that it is the presence of such coating which prevents abrasion of a wearing part by the incorporated glass. It is also believed that, at least in some instances, the lubricous coating can be considered as a stearic acid, or other higher fatty acid, derivative of glass. Most fiberizable glasses contain substantial amounts of calcium oxide. Calcium is known to form highly insoluble and relatively unreactive. stearates and the like. It is also known that various oxides as they exist in glass are capable of reaction with certain reagents; the presence of the tightly adhering, lubricous coating on the glass fibers, which coating is not dissolved by carbon tetrachloride and other solvents, is thought to be explained by chemical reaction between stearic or other higher fatty acid and the glass surface. That the presence of a tightly adhering lubricous coating on the glass fibers is necessary to produce an effective high temperature lubricant in accordance with the invention has been demonstrated. For example, when fine glass fibers approximately of a micron in diameter and varying in length from about 0.0003 to about 0.25 inch were mixed with a silicone fluid lubricant containing no higher fatty acid, the resulting composition was not an effective high temperature lubricant. Instead, the fibers abraded wearing surfaces substantially. Upon examination of the fibers no lubricous film was discovered.

In general, any lubricating silicone fluid can he emcordance with the invention. The higher fatty acid or higher fatty acid compound can be present in the silicone as received, or can be deliberately added thereto. The higher fatty acid compound is preferably a soap, and can be, for example, an aluminum-, calcium-, sodium-, 1ithium-, strontium-, barium-, lead-, magnesium-, or zincsoap of stearic-, oleic-, lauric-, palmitic-, or a naphthenicacid. Preferably, at least about 1 percent of a free higher fatty acid is also present in any fluid containing an acid compound. A high temperature lubricant according to the invention can be produced from such a lubricating fluid merely by dispersing appropriately sized glass fibers therein; within a very short period of time after dispersion of the fibers in the fluid a substantial increase in viscosity is noted, in many cases amounting to thixotropic gel formation. The resulting lubricant can then be put immediately into high temperature service. The previously discussed lubricous coating forms on the fibers sufficiently early in such high temperature service that appreciable abrasion of moving parts is prevented. Also, the lubricity of the composition is such that it can be used effectively at low temperatures. While silicone fluid lubricants containing a higher fatty acid or compound thereof are preferred for the reason that a lubricant in accordance with the invention can be produced therefrom with great facility by merely dispersing the fibers therein and placing in high temperature service, it will be appreciated that silicone fluids containing no higher fatty acid can be employed. For example, the lubricous coating can be applied to fibers by incorporating them in a fluid containing a higher fatty acid and heating, and the coated fibers so produced can then be separated from the fluid and mixed with a silicone fluid lubricant to produce a high temperature lubricant according to the invention. The lubricous coating can also be provided on glass fibers by heating in stearic or other higher fatty acid. if desired, a fatty acid compound can also be mixed with the stearic or other acid used for applying the lubricous coating. A lubricant produced by mixing such pre-coated fibers with the silicone fluid lubricant may have substantial advantages over one which includes a higher fatty acid, because the lubricating fluid can be selected to have any of various particularly desired properties, including chemical stability at extremely high temperatures.

Known lubricating silicone fluids are useful for preparation of the high-temperature lubricants of the invention. In general, these silicone fluid lubricants are or-gano-polysiloxanes of a basic molecular formula consisting essentially of repeated structural units of wherein R and R can be the same or different, and each represents a hydrocarbon or substituted hydrocarbon radical with a carbon atom thereof linked to the silicon atom, and x represents the number of repeated structural units. Frequently the hydrocarbons are lower aliphatic radicals, such as methyl, ethyl, propyl, butyl, and the like radicals, although molecular structures containing some alicyclic radicals such as cyclohexyl and cyclopentyl are known, and molecular structures containing some aryl and alkylary-l radicals such as phenyl, tolyl, and the like are quite common. Desirably for lubricating fluids, the molecular structures are substantially free from such reactive functional groups as hydroxyl, carboxyl, alkyl, and the like, although halogenated aryl radicals, such as chlorinated phenyl radicals, may be present to impart desirable high-temperature lubricating characteristics. The properties of the fluid vary depending upon the particular radicals, the value of x, and Whether the repeated structural units comprise a linear polymer or connect 4 to form a cyclic closed-ring structure. Most useful for lubricants are the linear polymers wherein the polymer chain is generally terminated by a trihydrocarbonsilyl radical, such as the trimethylsilyl radical, which is linked through oxygen to a silicon of the polymer chain, with radicals containing reactive functional groups being undesirable for termination of the polymer chain. Most silicone fluid lubricants comprise substantially a linear polymeric structure, although some cyclic structures may be present. Lubricating silicone fluids generally are mixtures of linear polysiloxanes of various chain lengths with the proportions of the same not readily deter-mined. Adequate identification of a particular polysiloxane to one skilled in the art is a description by name, as a particular hydrocarbon polysiloxane, such as dimethyl-polysiloxane and methylphenylpolysiloxane, and the average ratio or proportion of the various hydrocarbon radicals therein per silicon atom along with a mention of the viscosity or some other property to indicate the molecular Weight.- For high-temperature lubricating purposes a small amount of an antioxidant, such as p-arninophenol, may be present with the silicone fluid to inhibit gelation. A number of such antioxidants are taught in US. Patents Nos. 2,389,802to 2,389,807.

The following examples are presented solely for the purpose of further illustrating and disclosing the invention, and are in no Way to be construed as limitations thereon.

Example I A charge of 100 grams of glass fibers having an average diameter of about micron, and ranging in length from about /2 inch to about 5 inches are introduced into a heater of the type used in the paper industry for producing slurries of cellulose in water, together with a 15 gallon portion of water, and subjected to a beating and chopping action for a period of fifteen minutes. After such period of time the water and fibers are removed from the beater; water is drained from the fibers in a suction press; and the fibers are dried. The combined beating and chopping action reduces the length of the fibers to an average of about 0.001 inch, about percent of the fibers being between 0.0003 inch and 0.003 inch in length.

A 20 gram portion of the resulting chopped and dried fibers is mixed with about milliliters of a warm ethyl alcohol solution containing about 16 grams of stearic acid. Then there is added and mixed therewith about 650 grams of a silicone fluid lubricant, which is a linear dimethylpolysiloxane having a ratio of about two methyl groups per silicon atom and terminal trimethylsilyl groups and which has a viscosity of about 500' centipoises when measured at about 80 F. Chain-stopped silicone fluids of this type and their preparation are more particularly described in US Patents Nos. 2,469,888 and 2,469,890. The mixing is continued while the resulting admixture is heated sufliciently to drive off substantially all of the ethyl alcohol, whereupon about 10 grams of p-aminophenol is mixed therewith and the resulting composition passed through a 3-roll paint mill several times.

The resulting composition is used to lubricate a hearing operated at 10,000 revolutions per minute in an oven at about 450 F. After more than two hundred hours of operation, the bearing shows only negligible wear. A comparison composition, prepared in a similar manner except that no stearic acid is included therein, when used to lubricate a like bearing and tested in a like manner shows substantial wear Well before 200 hours of opera tion.

Example II 75 ,amounts thereof employed, the amounts of coated fibers mixed therewith, and operating characteristics are given in the following table:

e The glass fibers had a higher fatty acid (principally stcaric acid) lubncrous coating tightly adhered to at least a part of the surface of each of the fiber lengths.

b A tradename for a silicone fluid lubricant consisting essentially of a methylphenylpolysiloxane having nonreactive terminal groups, a ratio of about 1.1 methyl groups per silicon atom, and a ratio of about 0.9 phenyl groups per silicon atom, and having a pour point of 9 0., a viscosity at 25 O. of 500 centistokes, and a high temperature stability such that it may be held at 250 C. for over 1000 hours without gelation.

A tradename for a commercially available silicone fluid.

Amounts from about /2 to 15 percent by weight of the higher fatty acid coated glass fibers upon admixture with the polysiloxane silicone fluids employed in the preceding examples also provide superior high-temperature lubricants of increased viscosity at high temperatures.

Other lubricating silicone fluids admixed similarly with higher fatty acid coated glass fibers also yield like lubricants of increased viscosity at high temperatures. For example, there may be used chlorinated phenyl-methylpolysiloxane fluid lubricants and other polysiloxane fluid lubricants, such as DC-55'0' which is a methylphenylpolysiloxane having non-reactive terminal groups, a ratio of about 1.5 methyl groups per silicon atom, a ratio of about 0.5 phenyl group per silicon atom, and having a 57 F. flash point (open cup), a pour point of -8 F., and a viscosity at 25 C. of 100-150 centistokes.

It will be apparent that various changes and modifications can be made from the specific details discussed herein without departing from the spirit and scope of the attached claims.

What We claim is:

1. A lubricant consisting essentially of from about /2 percent to about 15 percent of short lengths of fibrous glass having diameters not greater than about 5 microns, a coating of a higher fatty acid on each of said lengths of fibrous glass, and a major amount of a silicone fluid lubricant, said coated lengths of fibrous glass being dispersed in said silicone fluid lubricant.

2. A lubricant consisting essentially of lengths of fibrous glass not greater than about 5 microns in diameter, and ranging in length from about 7.5 microns to about 6000 microns, a coating of a higher fatty acid chemically bonded to each of said lengths of fibrous glass,

- fluid lubricant, said coated lengths of fibrous glass being V dispersed in said organo-polysiloxane silicone fluid lubricant.

3. A lubricant consisting essentially of from about /2 percent to about 15 percent of lengths of fibrous glass not greater than about 5 microns in diameter, and ranging in length from about 7.5 microns to about 6000 microns, a coating of a higher fatty acid on each of said lengths of fibrous glass, and from about percent to about 99 /2 percent of an organo-polysiloxane silicone fluid lubricant, said coated lengths of fibrous glass being dispersed in said organo-polysiloxane silicone fluid lubricant.

4. A lubricant consisting essentially of from about /2 percent to about 15 percent of lengths of fibrous glass not greater than about 5 microns in diameter, and ranging in length from about 7.5 microns to about. 6000 microns, a coating of stearic acid on each of said lengths of fibrous glass, and from about 85 percent to about 99 /2 percent of a methylphenylpolysiloxane silicone fluid lubricant, said coated lengths of fibrous glass being dispersed in said methylphenylpolysilox-ane silicone fluid lubricant.

5. A lubricant consisting essentially of from about 2 percent to about 10 percent of lengths of fibrous glass not greater than about 5 microns in diameter, and ranging in length from about 7.5 microns to about 6000 microns, a coating of stearic acid on each of said lengths of fibrous glass, and from about percent to about 98 percent of a methylphenylpolysiloxane silicone fluid lubricant, said coated lengths of fibrous glass being dispersed in said methylphenylpolysiloxane silicone fluid tlubricant.

6. A lubricant consisting essentially of from about /2 percent to about 15 percent of glass fibers having a diameter from about 0.05 micron to about 5 microns, and ranging in length from about 7.5 microns to about 6000 microns, a coating of stearic acid on said glass fibers, and from about 85 percent to about 99 /2 percent of a dimethylpolysiloxane silicone fluid lubricant, said coated glass fibers being dispersed in said dimethylpolysiloxane silicone fluid lubricant.

7. A lubricant consisting essentially of from about A percent to about 15 percent of glass fibers having a diameter from about 0.05 micron to about 5 microns, and ranging in length from about 7.5 microns to about 6000 microns, a coating of stearic acid on said glass fibers, and from about 85 percent to about 99 /2 percent of a methylphenylpolysiloxane silicone fluid lubricant, said coated glass fibers being dispersed in said methylpheny lpoly siloxane silicone fluid lubricant.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LUBRICANT CONSISTING ESSENTIALLY OF FROM ABOUT 1/2 PERCENT TO ABOUT 15 PERCENT OF SHORT LENGTHS OF FIBROUS GLASS HAVING DIAMETERS NOT GREATER THAN ABOUT 5 MICRONS, A COATING OF A HIGHER FATTY ACID ON EACH OF SAID LENGTHS OF FIBROUS GLASS, AND A MAJOR AMOUNT OF A SILICONE FLUID LUBRICANT, SAID COATED LENGTHS OF FIBROUS GLASS BEING DISPERSED IN SAID SILICONE FLUID LUBRICANT. 